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  <div class="question_difficulty">
   难度：Medium
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   <h1 class="question_title">
    148. Sort List
   </h1>
   <p>
    Sort a linked list in
    <em>
     O
    </em>
    (
    <em>
     n
    </em>
    log
    <em>
     n
    </em>
    ) time using constant space complexity.
   </p>
   <p>
    <strong>
     Example 1:
    </strong>
   </p>
   <pre>
<strong>Input:</strong> 4-&gt;2-&gt;1-&gt;3
<strong>Output:</strong> 1-&gt;2-&gt;3-&gt;4
</pre>
   <p>
    <strong>
     Example 2:
    </strong>
   </p>
   <pre>
<strong>Input:</strong> -1-&gt;5-&gt;3-&gt;4-&gt;0
<strong>Output:</strong> -1-&gt;0-&gt;3-&gt;4-&gt;5</pre>
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   <h1 class="question_title">
    148. 排序链表
   </h1>
   <p>
    在&nbsp;
    <em>
     O
    </em>
    (
    <em>
     n
    </em>
    &nbsp;log&nbsp;
    <em>
     n
    </em>
    ) 时间复杂度和常数级空间复杂度下，对链表进行排序。
   </p>
   <p>
    <strong>
     示例 1:
    </strong>
   </p>
   <pre><strong>输入:</strong> 4-&gt;2-&gt;1-&gt;3
<strong>输出:</strong> 1-&gt;2-&gt;3-&gt;4
</pre>
   <p>
    <strong>
     示例 2:
    </strong>
   </p>
   <pre><strong>输入:</strong> -1-&gt;5-&gt;3-&gt;4-&gt;0
<strong>输出:</strong> -1-&gt;0-&gt;3-&gt;4-&gt;5</pre>
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